Semiconductor device

ABSTRACT

In a high-voltage semiconductor switching element, in addition to a first emitter region that is necessary for switching operations, a second emitter region, which is electrically connected with the first emitter region through a detection resistor in current detection means and is electrically connected with the current detection means, is formed. No emitter electrode is formed on the second emitter region, while an emitter electrode is formed on a part of a base region that is adjacent to the second emitter region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device including aninsulated gate switching element, and more particularly relates to asemiconductor device including an overcurrent protection circuit toprotect a switching element from an overcurrent.

2. Description of the Related Art

FIG. 12 shows a typical cross-sectional configuration of a lateralinsulated gate bipolar transistor (hereinafter referred to as an “IGBT”)which is used as a high-voltage semiconductor switching element. Asshown in FIG. 12, an N-type extended drain region 52 and a P-type baseregion 53 adjacent to the extended drain region 52 are formed in surfaceportions of a semiconductor substrate 51. An N⁺-type emitter region 54is formed in a surface portion of the base region 53 so as to be spacedapart from the extended drain region 52. A gate insulating film 56 isformed on the base region 53 so as to extend on a part of the emitterregion 54 and on a part of the extended drain region 52, and a gateelectrode 57 is formed on the gate insulating film 56. A P-typecollector region 58 is formed in a surface portion of the extended drainregion 52 so as to be spaced apart from the base region 53.

Moreover, the IGBT shown in FIG. 12 includes a collector terminal P1′electrically connected to the collector region 58, a gate terminal P2′electrically connected to the gate electrode 57, and an emitter terminalP3′ electrically connected to the emitter region 54.

The lateral IGBT shown in FIG. 12 is turned on when a forward biasvoltage is applied between the gate terminal P2′ and the emitterterminal P3′ with the collector terminal P1′ set to a high potential.Conversely, when a zero bias voltage or a reverse bias voltage isapplied between the gate terminal P2′ and the emitter terminal P3′, thelateral IGBT is turned off. In this manner, the lateral IGBT has aswitching characteristic in which the lateral IGBT is turned on and offin accordance with the gate voltage applied to the gate electrode 57.

A semiconductor device including such a lateral IGBT is often used withan inductive load connected between the collector terminal P1′ and apower supply. If a failure occurs in such a situation, the inductiveload is short-circuited, causing a current more than several times arated current to pass through the lateral IGBT. When the load is thusshort-circuited, it is necessary to sense the overcurrent so as tointerrupt the gate voltage or the collector voltage, because otherwisethere would be a thermal breakdown in the lateral IGBT due to thetemperature increase.

In view of this, a semiconductor device having an overcurrent protectionfunction for lateral IGBT shown in FIG. 13 has been proposed (see PatentDocument 1). The semiconductor device 10 shown in FIG. 13 includes alateral IGBT 1, which is a principal switching element controlled by agate voltage, and a current detection lateral IGBT 2 connected inparallel to the lateral IGBT 1. Respective gate electrodes of thelateral IGBTs are electrically connected to the gate terminal P2′,respective collector regions in the lateral IGBTs are electricallyconnected to the collector terminal P1′, and an emitter region in thelateral IGBT 1 as the principal switching element is electricallyconnected to the emitter terminal P3′. An emitter region in the currentdetection lateral IGBT 2 is connected with a sense resistor 23 as acurrent detection resistor. In the semiconductor device 10 shown in FIG.13, a current detection circuit 20, which is electrically connected withthe current detection lateral IGBT 2, includes a voltage comparator 21,a reference voltage circuit 22, and the aforementioned sense resistor23, both of which are connected with the voltage comparator 21. Therespective other ends of the reference voltage circuit 22 and the senseresistor 23 are electrically connected to the emitter terminal P3′.

In the semiconductor device 10 of FIG. 13, a current 9 passing throughthe current detection lateral IGBT 2 flows through the sense resistor 23to the emitter terminal P3′. As a result, a voltage generated betweenboth ends of the sense resistor 23 is compared with a voltage generatedby the reference voltage circuit 22 by the voltage comparator 21, and acurrent 8 passing through the lateral IGBT 1 as the principal switchingelement is controlled based on the thus obtained voltage difference.

-   [Patent Document 1] Japanese Laid-Open Publication No. 9-260592-   [Patent Document 2] Japanese Laid-Open Publication No. 7-297387

SUMMARY OF THE INVENTION

However, the conventional semiconductor device having the overcurrentprotection function for the lateral IGBT has a following problemdescribed below.

Specifically, in the semiconductor device 10 of FIG. 13, when thevoltage generated between both ends of the sense resistor 23 isincreased, the potential of the emitter region in the current detectionlateral IGBT 2 is increased, causing the current not to flow wellthrough the lateral IGBT 2 and thus preventing proper operation of theovercurrent protection function. In order to allow the overcurrentprotection function, i.e., the current detection circuit 20, to operateproperly, the voltage generated between both ends of the sense resistor23 must be limited to approximately 0.3 V at the most.

In the conventional semiconductor device 10 of FIG. 13, when the ratiobetween the current 9 passing through the sense resistor 23 and thecurrent 8 passing through the lateral IGBT 1 (i.e., the current 8/thecurrent 9) is designated as a sense ratio, the sense ratio is as smallas approximately 200, for example. Therefore, in a case in which theovercurrent protection function should operate when the value of thecurrent 8 reaches 4 A, for example, the value of the current 9 at thistime will be 20 mA. Thus, in order to make the voltage between both endsof the sense resistor 23 be 0.3 V or lower, the resistance value of thesense resistor 23 must be set as small as 15Ω or less. Nevertheless,when the sense resistor 23 is formed to have a small resistance value ofapproximately 15Ω, fabrication variation in the resistance value becomesso large that a current value (i.e., the value of the current 9 passingthrough the sense resistor 23) at which the overcurrent protectionfunction operates is also varied largely.

On the other hand, in order to increase the sense ratio, the size of thecurrent detection lateral IGBT 2 may be reduced to thereby lower thevalue of the current 9. In this case, however, the problem of increasedvariation in the value of the current 9, i.e., in the current value atwhich the overcurrent protection function operates, caused by thereduction in the size of the lateral IGBT 2, is again unavoidable.

That is, since the sense ratio cannot be sufficiently increased in theconventional semiconductor device having the overcurrent protectionfunction for the lateral IGBT, the resistance value of the senseresistor and the size of the current detection IGBT are unavoidablydesigned to be small, which results in the problem of increasedvariation in the current value at which the overcurrent protectionfunction operates.

In view of the foregoing problem, an object of the invention is toprovide a semiconductor device which has an overcurrent protectionfunction for a high-voltage semiconductor switching element and in whichvariation in a current value at which the overcurrent protectionoperates is reduced by increasing a ratio between a current passingthrough a sense resistor and a current passing through the high-voltagesemiconductor switching element.

In order to achieve the above object, a first inventive semiconductordevice includes: a high-voltage semiconductor switching elementcontrolled by a gate voltage applied to a gate electrode; and currentdetection means including a detection resistor capable of detecting partof current flowing through the high-voltage semiconductor switchingelement. The high-voltage semiconductor switching element includes: abase region of a second conductivity type formed in a semiconductorsubstrate of a first conductivity type; a first emitter region of thefirst conductivity type formed in the base region; a collector region ofthe second conductivity type formed in the semiconductor substrate so asto be spaced apart from the base region; a gate insulating film formedat least on a part of the base region located closer to the collectorregion with respect to the first emitter region; a gate electrode formedon the gate insulating film; a collector electrode formed above thesemiconductor substrate and electrically connected with the collectorregion; and an emitter electrode formed above the semiconductorsubstrate and electrically connected with both the base region and thefirst emitter region; a second emitter region, which is electricallyconnected with the first emitter region through the detection resistorand is electrically connected with the current detection means, is alsoformed in the base region; and the emitter electrode is not formed onthe second emitter region, while the emitter electrode is formed on apart of the base region that is adjacent to the second emitter region.

In the invention, the “high-voltage semiconductor switching element”means a switching element which has a breakdown voltage of approximately200 V or higher, for example, for a drain voltage when a gate voltage is0 V.

In the first inventive semiconductor device, the second emitter region,which is electrically connected with the current detection means and iselectrically connected with the first emitter region through thedetection resistor (a sense resistor) in the current detection means, isformed in the high-voltage semiconductor switching element, i.e., in alateral IGBT, in addition to the emitter region (the first emitterregion) that is necessary for switching operations. Also, the emitterelectrode is not formed on the second emitter region, while the emitterelectrode is formed on a part of the base region that is adjacent to thesecond emitter region. It is thus possible to prevent a hole current ofthe current passing through the lateral IGBT from flowing from thesecond emitter region to the sense resistor. In other words, only anelectron current passing through the second emitter region flows to thesense resistor. Hence, the current (a sense current) passing through thesense resistor can be reduced without designing the sense resistor witha small resistance value and the second emitter region of a small size.Thus, in the first inventive semiconductor device having the overcurrentprotection function for the high-voltage semiconductor switchingelement, the ratio between the current flowing from the second emitterregion to the sense resistor and the current flowing through thehigh-voltage semiconductor switching element, that is, a sense ratio,can be made twice as much or higher than that obtained in theconventional semiconductor device. As a result, the resistance value ofthe sense resistor and the size of the second emitter region can bedesigned to be larger, so that variations in the current value at whichthe overcurrent protection operates can be reduced.

In the first inventive semiconductor device, the semiconductor substrateis preferably of the second conductivity type; the semiconductor devicepreferably further includes a drift region of the first conductivitytype formed in the semiconductor substrate so as to be adjacent to thebase region; the first emitter region and the second emitter region arepreferably spaced apart from the drift region; and the collector regionis preferably formed in the drift region.

Then, as compared with a dopant concentration in the semiconductorsubstrate of the first conductivity type obtained when thatsemiconductor substrate is used, a dopant concentration in the driftregion of the first conductivity type can be increased and hence currentcapability in the high-voltage semiconductor switching element can beenhanced. Specifically, since the lifetime of minority carriers in thedrift region can be shortened by increasing the dopant concentration inthe drift region, the fall time of a collector current (i.e., the timerequired for the collector current to be off when the gate is off) canbe reduced.

A second inventive semiconductor device includes: a high-voltagesemiconductor switching element controlled by a gate voltage applied toa gate electrode; and current detection means including a detectionresistor capable of detecting part of current flowing through thehigh-voltage semiconductor switching element. The high-voltagesemiconductor switching element includes: a base region of a secondconductivity type formed in a semiconductor substrate of a firstconductivity type; a first emitter/source region of the firstconductivity type formed in the base region; a collector region of thesecond conductivity type formed in the semiconductor substrate so as tobe spaced apart from the base region; a drain region of the firstconductivity type formed in the semiconductor substrate so as to bespaced apart from the base region; a gate insulating film formed atleast on a part of the base region located closer to the collectorregion with respect to the first emitter/source region; a gate electrodeformed on the gate insulating film; a collector/drain electrode formedabove the semiconductor substrate and electrically connected with thecollector region and the drain region; and an emitter/source electrodeformed above the semiconductor substrate and electrically connected withboth the base region and the first emitter/source region; a secondemitter/source region, which is electrically connected with the firstemitter/source region through the detection resistor and is electricallyconnected with the current detection means, is also formed in the baseregion; and the emitter/source electrode is not formed on the secondemitter/source region, while the emitter/source electrode is formed on apart of the base region that is adjacent to the second emitter/sourceregion.

That is, in the second inventive semiconductor device, when a currentflowing through the high-voltage semiconductor switching element issmall, the high-voltage semiconductor switching element operates as aMISFET (a metal insulator semiconductor field effect transistor), andwhen the current flowing through the high-voltage semiconductorswitching element is large, the high-voltage semiconductor switchingelement operates as an IGBT. In the high-voltage semiconductor switchingelement, the second emitter/source region, which is electricallyconnected with the current detection means and is electrically connectedwith the first emitter/source region through the detection resistor (asense resistor) in the current detection means, is formed in addition tothe emitter/source region (the first emitter/source region) that isnecessary for the switching operations. Also, the emitter/sourceelectrode is not formed on the second emitter/source region, while theemitter/source electrode is formed on a part of the base region that isadjacent to the second emitter/source region. It is thus possible toprevent a hole current of the current passing through the high-voltagesemiconductor switching element from flowing from the secondemitter/source region to the sense resistor when the high-voltagesemiconductor switching element performs the IGBT operation. In otherwords, only an electron current passing through the secondemitter/source region flows to the sense resistor. Hence, the current (asense current) passing through the sense resistor can be reduced withoutdesigning the sense resistor with a small resistance value and thesecond emitter/source region of a small size. Thus, in the secondinventive semiconductor device having the overcurrent protectionfunction for the high-voltage semiconductor switching element, when thehigh-voltage semiconductor switching element performs the IGBToperation, the ratio between the current flowing from the secondemitter/source region to the sense resistor and the current flowingthrough the high-voltage semiconductor switching element, that is, asense ratio, can be made twice as much or higher than that obtained whenthe high-voltage semiconductor switching element performs the MISFEToperation or that obtained in the conventional semiconductor device. Asa result, the resistance value of the sense resistor and the size of thesecond emitter/source region can be designed to be larger, so thatvariations in the current value at which the overcurrent protectionoperates can be reduced.

In the second inventive semiconductor device, the semiconductorsubstrate is preferably of the second conductivity type; thesemiconductor device preferably further includes a drift region of thefirst conductivity type formed in the semiconductor substrate so as tobe adjacent to the base region; the first emitter/source region and thesecond emitter/source region are preferably spaced apart from the driftregion; and the collector region and the drain region are preferablyformed in the drift region.

Then, as compared with a dopant concentration in the semiconductorsubstrate of the first conductivity type obtained when thatsemiconductor substrate is used, a dopant concentration in the driftregion of the first conductivity type can be increased, and hencecurrent capability in the high-voltage semiconductor switching elementcan be enhanced. Specifically, since the lifetime of minority carriersin the drift region can be shortened by increasing the dopantconcentration in the drift region, the fall time of a collector current(i.e., the time required for the collector current to be off when thegate is off) can be reduced. In addition, the ON resistance during theMISFET operation can be reduced by increasing the dopant concentrationin the drift region, thereby permitting a greater collector current toflow during the MISFET operation as compared with the case in which thesemiconductor substrate of the first conductivity type is used.

In the second inventive semiconductor device, the collector region andthe drain region each preferably include a plurality of separate parts;and each part of the collector region and each part of the drain regionare preferably located alternately so as to be in contact with eachother in a direction perpendicular to a direction going from thecollector region to the first emitter/source region.

In this way, in the high-voltage semiconductor switching element, byplacing each part of the drain region of the first conductivity typeperpendicularly to the direction going from the collector region of thesecond conductivity type to the first emitter/source region of the firstconductivity type, the length, i.e., the cell pitch, of each part of thecollector region that is necessary for the high-voltage semiconductorswitching element to switch from the MISFET operation to the IGBToperation can be reduced as compared with a case in which each part ofthe drain region is located in parallel to the direction going from thecollector region to the first emitter/source region.

Also, in this case, by changing the location of the secondemitter/source region in the high-voltage semiconductor switchingelement in accordance with the location of the drain region of the firstconductivity type and the location of the collector region of the secondconductivity type, the ratio between the current that flows from thesecond emitter/source region to the detection resistor and the currentthat flows through the high-voltage semiconductor switching element whenthe high-voltage semiconductor switching element performs the IGBToperation can be changed at will without changing the size of the secondemitter/source region.

Specifically, if the second emitter/source region and the collectorregion are located so as to face each other with a part of the baseregion interposed therebetween, it is possible to reduce a differencebetween the ratio between the current that flows from the secondemitter/source region to the detection resistor and the current thatflows through the high-voltage semiconductor switching element when thehigh-voltage semiconductor switching element performs the MISFEToperation and the ratio between the current that flows from the secondemitter/source region to the detection resistor and the current thatflows through the high-voltage semiconductor switching element when thehigh-voltage semiconductor switching element performs the IGBT operationas compared with a case in which the second emitter/source region andthe drain region are located so as to face each other with a part of thebase region interposed therebetween. Hence, a control circuit that dealswith sense ratio variations can be configured easily, and thus whenovercurrent protection is performed based on the current passing throughthe second emitter/source region, the current passing through thehigh-voltage semiconductor switching element is controlled moreprecisely.

Furthermore, if the second emitter/source region and the drain regionare located so as to face each other with a part of the base regioninterposed therebetween, it is possible to increase the differencebetween the ratio between the current that flows from the secondemitter/source region to the detection resistor and the current thatflows through the high-voltage semiconductor switching element when thehigh-voltage semiconductor switching element performs the MISFEToperation and the ratio between the current that flows from the secondemitter/source region to the detection resistor and the current thatflows through the high-voltage semiconductor switching element when thehigh-voltage semiconductor switching element performs the IGBT operationas compared with the case in which the second emitter/source region andthe collector region are located so as to face each other with a part ofthe base region interposed therebetween. That is, since the sense ratiocan be increased further, the resistance value of the sense resistor andthe size of the second emitter/source region can be designed to belarger, so that variations in the current value at which the overcurrentprotection operates can be reduced.

As set forth above, the invention relates to a semiconductor deviceincluding an insulated gate switching element. More particularly, whenapplied to a semiconductor device that includes an overcurrentprotection circuit to protect a switching element from an overcurrent,the invention produces an excellent effect, in which variations in acurrent value at which the overcurrent protection operates are reducedby increasing the ratio between a current flowing through a senseresistor and a current flowing through the high-voltage semiconductorswitching element, and is thus very beneficial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating the configuration of asemiconductor device according to first, second, and third embodimentsof the invention.

FIG. 2 is a plan view illustrating the configuration of thesemiconductor device according to the first embodiment of the invention.

FIG. 3 is a cross-sectional view taken along the line A-A′ in FIG. 2.

FIG. 4 is a cross-sectional view taken along the line B-B′ in FIG. 2.

FIG. 5 is a cross-sectional view taken along the line C-C′ in FIG. 2.

FIG. 6 is a plan view illustrating the configuration of thesemiconductor device according to the second embodiment of theinvention.

FIG. 7 is a cross-sectional view taken along the line F-F′ in FIG. 6.

FIG. 8 is a cross-sectional view taken along the line G-G′ in FIG. 6.

FIG. 9 shows, for comparison purposes, sense ratio variations withrespect to collector currents flowing through high-voltage semiconductorswitching elements in the semiconductor devices according to the secondand third embodiments of the invention.

FIG. 10 is a plan view illustrating the configuration of thesemiconductor device according to the third embodiment of the invention.

FIG. 11 is a cross-sectional view taken along the line K-K′ in FIG. 10.

FIG. 12 is a cross-sectional view of a conventional lateral IGBT.

FIG. 13 is a circuit diagram of a conventional semiconductor devicehaving an overcurrent protection function for a lateral IGBT.

FIG. 14 is a plan view illustrating the configuration of a semiconductordevice as a comparison example.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

A semiconductor device, specifically, a semiconductor device having ahigh-voltage semiconductor switching element and an overcurrentprotection function for the element, according to a first embodiment ofthe invention will be described with reference to the accompanyingdrawings.

FIG. 1 shows the rough circuit configuration of the semiconductor deviceof this embodiment. As shown in FIG. 1, the semiconductor device 150 ofthis embodiment includes a high-voltage semiconductor switching element100 composed of a lateral IGBT controlled by a gate voltage applied to agate electrode. A collector region in the high-voltage semiconductorswitching element 100 is electrically connected to a collector terminal(a collector electrode) P1, while a gate electrode of the high-voltagesemiconductor switching element 100 is electrically connected with agate terminal P2. As a characteristic of the semiconductor device ofthis embodiment, a part (hereinafter referred to as a “second emitterregion 110”) of an emitter region in the high-voltage semiconductorswitching element 100 is connected with a sense resistor 123 acting as acurrent detection resistor, and the other part (hereinafter referred toas a “first emitter region 104”) of the emitter region is electricallyconnected with an emitter terminal (an emitter electrode) P3. In thesemiconductor device of this embodiment, a current detection circuit120, which is electrically connected with the second emitter region 110,includes a voltage comparator 121, a reference voltage circuit 122, andthe aforementioned sense resistor 123, both of which are connected tothe voltage comparator 121. The other terminals of the reference voltagecircuit 122 and the sense resistor 123 are electrically connected to theemitter terminal P3. In other words, the second emitter region 110 andthe first emitter region 104 are electrically connected with each otherthrough the sense resistor 123.

FIG. 2 is a plan view of the high-voltage semiconductor switchingelement 100 in the semiconductor device 150 of this embodimentillustrated in FIG. 1, and FIGS. 3 to 5 are cross-sectional views takenalong the lines A-A′, B-B′, and C-C′ in FIG. 2, respectively.

The high-voltage semiconductor switching element 100 shown in FIGS. 2 to5, i.e., a lateral IGBT according to this embodiment, is configured inthe following manner. An N-type extended drain region (a drift region)102 having a dopant concentration of approximately 1×10¹⁶/cm³, forexample, and a P-type base region 103 having a dopant concentration ofapproximately 1×10¹⁷/cm³, for example, which is adjacent to the extendeddrain region 102, are formed in surface portions of a P⁻-typesemiconductor substrate 101 having a dopant concentration ofapproximately 1×10¹⁴/cm³, for example. An N⁺-type first emitter region104 having a dopant concentration of approximately 1×10²⁰/cm³, forexample, is formed in surface portions of the base region 103 so as tobe spaced apart from the extended drain region 102. Also, a P⁺-type basecontact region 105 having a dopant concentration of approximately1×10¹⁹/cm³, for example, is formed in surface portions of the baseregion 103 so as to be in contact with the first emitter region 104, andthe base region 103 and the first emitter region 104 are electricallyconnected with each other through the base contact region 105. A gateinsulating film 106 is formed on the base region 103 so as to extend onpart of the first emitter region 104 and on a part of the extended drainregion 102, and a gate electrode 107 is formed on the gate insulatingfilm 106. A P⁺-type collector region 108 having a dopant concentrationof approximately 1×10¹⁹/cm³, for example, is formed in a surface portionof the extended drain region 102 so as to be spaced apart from the baseregion 103.

In this embodiment, the first emitter region 104 and the base contactregion 105 are composed of separate parts, and each part of the firstemitter region 104 and each part of the base contact region 105 arelocated alternately so as to be in contact with each other in adirection perpendicular to a direction going from the base region 103 tothe collector region 108. As a characteristic of this embodiment, asstated above, parts of the first emitter region 104 are replaced withthe second emitter region 110, and the second emitter region 110 isconnected with the first emitter region 104 through the sense resistor123 having a resistance of approximately 70Ω, for example. Also, anemitter electrode is formed on the first emitter region 104 and on thebase contact region 105 (including parts adjacent to the second emitterregion 110), while the emitter electrode is not formed on the secondemitter region 110.

It should be noted that in the semiconductor device 150 of thisembodiment shown in FIGS. 1 to 5, part of the base contact region 105adjacent to the second emitter region 110 and part of the base contactregion 105 adjacent to the first emitter region 104 are all connectedwith the first emitter region 104 through the emitter electrode (theemitter terminal P3). The sense resistor 123 is connected between thefirst emitter region 104 and the second emitter region 110. In otherwords, the sense resistor 123 is connected between the second emitterregion 110 and the first emitter and base contact region 104 and 105,the base contact region 105 being electrically connected with the firstemitter region 104 through the emitter electrode. Since the base region103 is electrically connected with the first emitter region 104 throughthe base contact region 105 and the emitter electrode, the potential ofthe base region 103 is the same as that of the first emitter region 104.

Due to this characteristic, of the current passing through thehigh-voltage semiconductor switching element 100, an entire hole currentflows as a current 11 (see FIG. 1) from the base region 103 through thebase contact region 105 to the emitter terminal P3. That is, it ispossible to prevent the hole current of the current passing through thehigh-voltage semiconductor switching element 100 from flowing from thesecond emitter region 110 to the sense resistor 123. On the other hand,only an electron current passing through the second emitter region 110flows as a sense current 13 to the emitter terminal P3 through the senseresistor 123. And a voltage generated between both ends of the senseresistor 123 is compared with a voltage generated by the referencevoltage circuit 122 by the voltage comparator 121, and a current (i.e.,a current 12 in FIG. 1) passing through the high-voltage semiconductorswitching element 100 as the principal switching element is controlledbased on the thus obtained voltage difference.

As described above, in the semiconductor device 150 of this embodimentunlike in the conventional example, since the hole current 11 passingthrough the high-voltage semiconductor switching element 100 does notflow through the sense resistor 123, the sense current 13 is reduced byan amount corresponding to the hole current 11. That is, when the ratiobetween the sense current 13 passing through the sense resistor 123 andthe current 12 passing through the high-voltage semiconductor switchingelement 100 is designated as a sense ratio, the sense ratio can beincreased in the semiconductor device 150 of this embodiment as comparedwith the conventional example.

The results of an experiment actually made by the present inventors showthat under conditions in which the conventional semiconductor devicewould have a sense ratio of approximately 300, when a base region in acurrent detection IGBT (i.e., parts of the base region 103 adjacent tothe second emitter region 110) was electrically connected with anemitter region (i.e., the first emitter region 104) in an IGBT servingas a principal switching element as in this embodiment, a sense ratiowas substantially doubled to approximately 600.

Thus, in the semiconductor device 150 having the overcurrent protectionfunction for the high-voltage semiconductor switching element accordingto this embodiment, since the sense ratio can be increased as comparedwith the conventional semiconductor device, the resistance value of thesense resistor 123 and the size of the second emitter region 110 can bedesigned to be larger, so that variations in the current value at whichthe overcurrent protection operates can be reduced.

In this embodiment, the N-type extended drain region (the drift region)102 is formed, and the P-type collector region 108 is formed in theN-type extended drain region 102. Instead of this formation, a P-typecollector region may be formed in an N-type semiconductor substratewithout forming the extended drain region 102. However, in the case inwhich the N-type extended drain region 102 is formed, a dopantconcentration can be increased and hence current capability in thehigh-voltage semiconductor switching element can be enhanced as comparedwith cases in which an N-type semiconductor substrate is used.Specifically, since the lifetime of minority carriers in the extendeddrain region 102, i.e., in the drift region, can be shortened byincreasing the dopant concentration in the drift region, the fall timeof a collector current (i.e., the time required for the collectorcurrent to be off when the gate is off) can be reduced.

Also, in this embodiment, the gate insulating film 106 is formed on thebase region 103 so as to extend on part of the first emitter region 104and on a part of the extended drain region 102. However, it would besufficient if the gate insulating film 106 is formed at least on a partof the base region 103 located closer to the collector region 108 withrespect to the first emitter region 104.

COMPARISON EXAMPLE

A semiconductor device as a comparison example (see Patent Document 2)will be described with reference to the accompanying drawings.

FIG. 14 is a plan view of the semiconductor device as the comparisonexample, specifically, the lateral IGBT 1 as the principal switchingelement and the current detection lateral IGBT 2 in the conventionalsemiconductor device shown in FIG. 13. A cross-sectional view takenalong the line Z-Z′ in FIG. 14 corresponds to FIG. 12 (a cross-sectionalconfiguration of the conventional lateral IGBT). In FIG. 14, the samemembers as those shown in FIG. 12 or 13 are identified by the samereference numerals, and duplicated descriptions will be thus omittedherein.

As s shown in FIG. 14, in the lateral IGBT 1 as the principal switchingelement in the semiconductor device as the comparison example, a basecontact region 55 is formed in a surface portion of the base region 53so as to be in contact with emitter region 54, and the base region 53and the emitter region 54 are electrically connected with each otherthrough the base contact region 55. The emitter region 54 and the basecontact region 55 are composed of separate parts, and each part of theemitter region 54 and each part of the base contact region 55 arelocated alternately so as to be in contact with each other in adirection perpendicular to a direction going from the base region 53 tothe collector region 58.

In the comparison example, parts of the emitter region 54 are replacedwith an emitter region 60 for the lateral IGBT 2, and parts of the basecontact region 55 are replaced with a base contact region 61 for thelateral IGBT 2. That is, the configuration of the current detectionlateral IGBT 2 is the same as that of the lateral IGBT 1 as theprincipal switching element, but the size of the lateral IGBT 2 issmaller than that of the lateral IGBT 1.

Furthermore, in the comparison example, the emitter region 60 and thebase contact region 61 are both connected with the emitter region 54 andthe base contact region 55 in the lateral IGBT 1 through the senseresistor 23.

As described above, in the comparison example unlike in the firstembodiment, the emitter electrode is not formed on the emitter region 60for the lateral IGBT 2 nor on the base contact region 61. In otherwords, the emitter electrode is formed only on the emitter region 54 forthe lateral IGBT 1 and on the base contact region 55. As a result, ofthe current passing through the lateral IGBT 2, a hole current togetherwith an electron current passing through second emitter region 110 alsoflows through the sense resistor 23 to the emitter terminal P3′ as thesense current 9 (see FIG. 13). Therefore, unlike in the firstembodiment, the sense current 9 cannot be reduced and hence the senseratio cannot be increased. Consequently, the resistance value of thesense resistor 23 and the size of the current detection lateral IGBT 2are unavoidably designed to be small, resulting in the problem ofincreased variation in the current value at which the overcurrentprotection function operates.

Second Embodiment

A semiconductor device, specifically, a semiconductor device having ahigh-voltage semiconductor switching element and an overcurrentprotection function for the element, according to a second embodiment ofthe invention will be described with reference to the accompanyingdrawings. The rough circuit configuration of the semiconductor device ofthis embodiment is the same as that of the first embodiment shown inFIG. 1, and duplicated descriptions will be thus omitted herein.However, in this embodiment, the first emitter region 104 should be readas a first emitter/source region 104, the second emitter region 110 as asecond emitter/source region 110, the collector terminal P1 as acollector/drain terminal (a collector/drain electrode) P1, and theemitter terminal P3 as an emitter/source terminal (an emitter/sourceelectrode) P3.

FIG. 6 is a plan view of the high-voltage semiconductor switchingelement 100 in the semiconductor device 150 of FIG. 1 according to thisembodiment, and FIGS. 7 and 8 are cross-sectional views taken along thelines F-F′ and G-G′ in FIG. 6, respectively. A cross-sectional viewtaken along the line D-D′ in FIG. 6 is the same as the cross sectionalview in the first embodiment shown in FIG. 4, and a cross-sectional viewtaken along the line E-E′ in FIG. 6 is the same as the cross sectionalview in the first embodiment shown in FIG. 5. The semiconductor device150 of this embodiment has the same configuration as the semiconductordevice of the first embodiment except for the configuration of thehigh-voltage semiconductor switching element 100. Thus, in FIGS. 6 to 8,the same members as those of the first embodiment shown in FIGS. 2 to 5are identified by the same reference numerals, and duplicateddescriptions will be omitted herein.

The high-voltage semiconductor switching element 100 of this embodimentshown in FIGS. 6 to 8 differs from that of the first embodiment in thefollowing respects: an N⁺-type drain region 109 having a dopantconcentration of approximately 1×10²⁰/cm³, for example, is formed in asurface portion of an extended drain region 102 so as to be spaced apartfrom a base region 103. Also, a collector region 108 and the drainregion 109 are composed of separate parts, and each part of thecollector region 108 and each part of the drain region 109 are locatedalternately so as to be in contact with each other in a directionperpendicular to a direction going from the collector region 108 to afirst emitter/source region 104. The collector region 108 and the drainregion 109 are electrically connected with a collector/drain terminalP1.

In the high-voltage semiconductor switching element 100 according tothis embodiment, when a positive bias (hereinafter referred to as a“collector voltage”) is applied between the collector/drain terminal P1and an emitter/source terminal P3, current starts to flow from theN⁺-type drain region 109 through the N-type extended drain region 102and the P-type base region 103 to the first emitter/source region 104and to second emitter/source region 110 (hereinafter the current thatflows to the first emitter/source region 104 will be called a collectorcurrent 12, and the current that flows to the second emitter/sourceregion 110 will be called a sense current 13 (see FIG. 1)). At thistime, only electrons flow through the high-voltage semiconductorswitching element 100, which means that the high-voltage semiconductorswitching element 100 performs a MISFET operation. Next, as thecollector voltage is increased, the collector current 12 and the sensecurrent 13 are increased to some extent. And when the potentialdifference between the P⁺-type collector region 108 and part of theN-type extended drain region 102 located in the vicinity of thecollector region 108 is lowered to approximately 0.6 V, for example,holes are introduced into the extended drain region 102 from thecollector region 108, causing the operation of the high-voltagesemiconductor switching element 100 to be switched to an IGBT operation.

When the high-voltage semiconductor switching element 100 performs theMISFET operation, current flows from the N⁺-type drain region 109completely due to electrons, and all of the current flows to the firstemitter/source region 104 and to the second emitter/source region 110.Thus, the sense ratio is determined by the sizes of the firstemitter/source region 104 and of the second emitter/source region 110.

On the other hand, when the high-voltage semiconductor switching element100 performs the IGBT operation, part of the holes introduced from theP⁺-type collector region 108 into the N-type extended drain region 102flows from the P-type base region 103 through P⁺-type base contactregion 105 to the emitter/source terminal P3 as a hole current 11 (seeFIG. 1). That is, as in the first embodiment, it is possible to preventthe hole current of the current passing through the high-voltagesemiconductor switching element 100 from flowing from the secondemitter/source region 110 into a sense resistor 123. This allows thesense ratio obtained when the IGBT operation is performed to beincreased as compared with that obtained when the MISFET operation isperformed.

As set forth above, in the high-voltage semiconductor switching element100 in the semiconductor device 150 according to this embodiment, thesecond emitter/source region 110, which are electrically connected witha current detection means 120 and electrically connected with the firstemitter/source region 104 through the sense resistor 123 in the currentdetection means 120, is formed in addition to the first emitter/sourceregion 104 that are necessary for the switching operation. Also, theemitter/source electrode is not formed on the second emitter/sourceregion 110, while the emitter/source electrode is formed on parts of thebase region 103 (i.e., the base contact region 105) adjacent to thesecond emitter/source region 110. Therefore, when the high-voltagesemiconductor switching element 100 performs the IGBT operation, it ispossible to prevent the hole current 11 of the current passing throughthe high-voltage semiconductor switching element 100 from flowing fromthe second emitter/source region 110 to the sense resistor 123. That is,both when the MISFET operation is performed and when the IGBT operationis performed, only the electron current passing through the secondemitter/source region 110 flows through the sense resistor 123 to theemitter/source terminal P3 as the sense current 13. And a voltagegenerated between both ends of the sense resistor 123 is compared with avoltage generated by a reference voltage circuit 122 by a voltagecomparator 121, and the current (namely the current 12 in FIG. 1)passing through the high-voltage semiconductor switching element 100 asthe principal switching element is controlled based on the thus obtainedvoltage difference.

Hence, the current (the sense current 13) passing through the senseresistor 123 can be reduced without designing the sense resistor 123with a small resistance value and the second emitter/source region 110of a small size. Thus, in the semiconductor device 150 having theovercurrent protection function for the high-voltage semiconductorswitching element 100 according to this embodiment, when thehigh-voltage semiconductor switching element 100 performs the IGBToperation, the ratio between the current 13 flowing from the secondemitter/source region 110 to the sense resistor 123 and the current 12flowing through the high-voltage semiconductor switching element 100,that is, a sense ratio, can be made twice as much or higher than thatobtained when the high-voltage semiconductor switching element 100performs the MISFET operation or that obtained in the conventionalsemiconductor device. As a result, the resistance value of the senseresistor 123 and the size of the second emitter/source region 110 can bedesigned to be larger, so that variations in the current value at whichthe overcurrent protection operates can be reduced.

Furthermore, in this embodiment, the collector region 108 and the drainregion 109 are composed of separate parts, and each part of thecollector region 108 and each part of the drain region 109 are locatedalternately so as to be in contact with each other in the directionperpendicular to the direction going from the collector region 108 tothe first emitter/source region 104. It is thus possible to reduce thelength, i.e., the cell pitch, of each part of the collector region 108that is necessary for the high-voltage semiconductor switching element100 to switch from the MISFET operation to the IGBT operation ascompared with a case in which each part of the drain region 109 islocated in parallel to the direction going from the collector region 108to the first emitter/source region 104.

In this embodiment, by changing the location of the secondemitter/source region 110 in the high-voltage semiconductor switchingelement 100 in accordance with the locations of the drain region 109 andof the collector region 108, the ratio between the current 13 that flowsfrom the second emitter/source region 110 to the detection resistor 123and the current 12 that flows through the high-voltage semiconductorswitching element 100 when the high-voltage semiconductor switchingelement 100 performs the IGBT operation can be changed at will withoutchanging the size of the second emitter/source region 110. The reasonsfor this are as follows. The amount of electrons emitted from theN⁺-type emitter/source region 104 or 110 that faces the P⁺-typecollector region 108 with the base region 103 interposed therebetween isgreater than the amount of electrons emitted from the N⁺-typeemitter/source region 104 or 110 that faces the N⁺-type drain region 109with the base region 103 interposed therebetween. Specifically, of theelectrons emitted from the N⁺-type emitter/source region 104 or 110,some electrons flow to the N⁺-type drain region 109 due to the MISFEToperation, and the other electrons recombine with holes introduced fromthe P⁺-type collector region 108 into the N-type extended drain region102. On the other hand, more holes are present in parts of the N-typeextended drain region 102 located close to the P⁺-type collector region108 as compared with parts of the N-type extended drain region 102located close to the N⁺-type drain region 109. Thus, the N⁺-typeemitter/source region 104 or 110 facing the P⁺-type collector region 108emits more electrons than the N⁺-type emitter/source region 104 or 110facing the N⁺-type drain region 109. Since the sense current isdetermined by the amount of electrons emitted from the secondemitter/source region 110, the value of the sense current (the current13) is adjustable by the location of the N⁺-type second emitter/sourceregion 110 with respect to the locations of the drain region 109 and ofthe collector region 108. Hence, the ratio between the current 13 thatflows from the second emitter/source region 110 to the detectionresistor 123 and the current 12 that flows through the high-voltagesemiconductor switching element 100 when the high-voltage semiconductorswitching element 100 performs the IGBT operation can be changed at willwithout changing the size of the second emitter/source region 110.

To be specific, in this embodiment, as shown in FIG. 6, the N⁺-typesecond emitter/source region 110 faces the P⁺-type collector region 108with the P-type base region 103 and the N-type extended drain 102interposed therebetween. In this case, the current (the sense current13) flowing through the second emitter/source region 110 is increased ascompared with a case in which the second emitter/source region 110 facesthe N⁺-type drain region 109 with the base region 103 and the extendeddrain 102 interposed therebetween. It is thus possible to lower thesense ratio obtained when the high-voltage semiconductor switchingelement 100 performs the IGBT operation.

FIG. 9 shows the relation between collector current flowing throughhigh-voltage semiconductor switching element and sense ratio, obtainedby the present inventors from their experiment. In FIG. 9, the opensquares indicate the result obtained for the high-voltage semiconductorswitching element of this embodiment, and the solid squares representthe result obtained for a high-voltage semiconductor switching elementaccording to a third embodiment which will be described later. As shownin FIG. 9, the sense ratio has values of approximately 300 in a MISFEToperation region 112 in which collector voltage (voltage applied to thecollector/drain electrode) is low and the collector current is small,whereas in an IGBT operation region 113, the sense ratio has values ofare approximately 600 and the variations from the sense ratio in theMISFET operation region 112 are smaller as compared to an IGBT operationregion 114 of the third embodiment which will be described later. Thismeans that variations in the collector current 12 with respect tovariations in the sense current 13 are small, and therefore, a controlcircuit that deals with sense ratio variations can be configured easily.Consequently, when overcurrent protection is performed based on thesense current 13, that is, the current passing through the secondemitter/source region 110, the collector current 12, that is, thecurrent passing through the high-voltage semiconductor switching element100, is controlled more precisely.

In this embodiment, the N-type extended drain region (the drift region)102 is formed, and the P-type collector region 108 and the N-type drainregion 109 are formed in the N-type extended drain region 102. Insteadof this formation, a P-type collector region and an N-type drain regionmay be formed in an N-type semiconductor substrate without forming theextended drain region 102. However, in the case in which the N-typeextended drain region 102 is formed, a dopant concentration can beincreased and hence current capability in the high-voltage semiconductorswitching element can be enhanced as compared with cases in which anN-type semiconductor substrate is used. Specifically, since the lifetimeof minority carriers in the extended drain region 102, i.e., in thedrift region, can be shortened by increasing the dopant concentration inthe drift region, the fall time of the collector current (i.e., the timerequired for the collector current to be off when the gate is off) canbe reduced. In addition, the ON resistance during the MISFET operationcan be reduced by increasing the dopant concentration in the driftregion, thereby permitting a greater collector current to flow duringthe MISFET operation as compared with cases in which an N-typesemiconductor substrate is used.

Also, in this embodiment, a gate insulating film 106 is formed on thebase region 103 so as to extend on part of the first emitter/sourceregion 104 and on a part of the extended drain region 102. However, itwould be sufficient if the gate insulating film 106 is formed at leaston a part of the base region 103 located closer to the collector region108 with respect to the first emitter/source region 104.

Third Embodiment

A semiconductor device, specifically, a semiconductor device having ahigh-voltage semiconductor switching element and an overcurrentprotection function for the element, according to a third embodiment ofthe invention will be described with reference to the accompanyingdrawings. The rough circuit configuration of the semiconductor device ofthis embodiment is the same as that of the first embodiment shown inFIG. 1, and duplicated descriptions will be thus omitted herein.However, in this embodiment, the first emitter region 104 should be readas a first emitter/source region 104, the second emitter region 110 as asecond emitter/source region 110, the collector terminal P1 as acollector/drain terminal (a collector/drain electrode) P1, and theemitter terminal P3 as an emitter/source terminal (an emitter /sourceelectrode) P3.

FIG. 10 is a plan view of the high-voltage semiconductor switchingelement 100 in the semiconductor device 150 of FIG. 1 according to thisembodiment, and FIG. 11 is a cross-sectional view taken along the lineK-K′ in FIG. 10. A cross-sectional view taken along the line H-H′ inFIG. 10 is the same as the cross sectional view in the first embodimentshown in FIG. 3, a cross-sectional view taken along the line I-I′ inFIG. 10 is the same as the cross sectional view in the first embodimentshown in FIG. 4, and a cross-sectional view taken along the line J-J′ inFIG. 10 is the same as the cross sectional view in the second embodimentshown in FIG. 8. The semiconductor device 150 of this embodiment has thesame configuration as the semiconductor devices of the first and secondembodiments except for the configuration of the high-voltagesemiconductor switching element 100. Thus, in FIGS. 10 and 11, the samemembers as those in the first embodiment shown in FIGS. 2 to 5 or asthose in the second embodiment shown in FIGS. 6 to 8 are identified bythe same reference numerals, and duplicated descriptions will be omittedherein.

In this embodiment, the effect obtained in the second embodiment isbasically achievable. To be specific, in the semiconductor device 150having the overcurrent protection function for the high-voltagesemiconductor switching element 100 according to this embodiment, whenthe high-voltage semiconductor switching element 100 performs an IGBToperation, the ratio between a current 13 flowing from secondemitter/source region 110 to a sense resistor 123 and a current 12flowing through the high-voltage semiconductor switching element 100,that is, a sense ratio, can be made twice as much or higher than thatobtained when the high-voltage semiconductor switching element 100performs a MISFET operation or that obtained in the conventionalsemiconductor device. As a result, the resistance value of the senseresistor 123 and the size of the second emitter/source region 110 can bedesigned to be larger, so that variations in the current value at whichthe overcurrent protection operates can be reduced. It is also possibleto reduce the length, i.e., the cell pitch, of each part of thecollector region 108 which is necessary for the high-voltagesemiconductor switching element 100 to switch from the MISFET operationto the IGBT operation.

Furthermore, in this embodiment as in the second embodiment, by changingthe location of the second emitter/source region 110 in the high-voltagesemiconductor switching element 100 in accordance with the locations ofthe drain region 109 and of the collector region 108, the ratio betweenthe current 13 that flows from the second emitter/source region 110 tothe detection resistor 123 and the current 12 that flows through thehigh-voltage semiconductor switching element 100 when the high-voltagesemiconductor switching element 100 performs the IGBT operation can bechanged at will without changing the size of the second emitter/sourceregion 110.

Specifically, in this embodiment, as shown in FIG. 10, the N⁺-typesecond emitter/source region 110 faces the N⁺-type drain region 109 witha P-type base region 103 and an N-type extended drain region 102interposed therebetween. In this case, the current (the sense current13) flowing through the second emitter/source region 110 is decreased ascompared with a case in which the second emitter/source region 110 facesthe P⁺-type collector region 108 with the base region 103 and theextended drain region 102 interposed therebetween. It is thus possibleto increase the sense ratio obtained when the high-voltage semiconductorswitching element 100 performs the IGBT operation.

FIG. 9 shows the relation between the collector currents flowing throughthe high-voltage semiconductor switching element and the sense ratio,obtained by the present inventors from their experiment. In FIG. 9, theopen squares indicate the result obtained for the high-voltagesemiconductor switching element of the second embodiment set forthabove, and the solid squares represent the result obtained for thehigh-voltage semiconductor switching element of this embodiment. Asshown in FIG. 9, in the IGBT operation region 114 of this embodiment,the sense ratio has values of approximately 800 and is thus increased ascompared to the IGBT operation region 113 of the above-described secondembodiment. That is, the sense ratio is increased further, andtherefore, in the semiconductor device 150 having the overcurrentprotection function for the high-voltage semiconductor switching element100 according to this embodiment, the resistance value of the senseresistor 123 and the size of the second emitter/source region 110 (i.e.,the current detection IGBT) can be designed to be larger, so thatvariations in the current value at which the overcurrent protectionoperates can be reduced further.

In this embodiment, the N-type extended drain region (the drift region)102 is formed, and the P-type collector region 108 and the N-type drainregion 109 are formed in the N-type extended drain region 102. Insteadof this formation, a P-type collector region and an N-type drain regionmay be formed in an N-type semiconductor substrate without forming theextended drain region 102. However, in the case in which the N-typeextended drain region 102 is formed, a dopant concentration can beincreased and hence current capability in the high-voltage semiconductorswitching element can be enhanced as compared with cases in which anN-type semiconductor substrate is used. Specifically, since the lifetimeof minority carriers in the extended drain region 102, i.e., in thedrift region, can be shortened by increasing the dopant concentration inthe drift region, the fall time of the collector current (i.e., the timerequired for the collector current to be off when the gate is off) canbe reduced. In addition, the ON resistance during the MISFET operationcan be reduced by increasing the dopant concentration in the driftregion, thereby permitting a greater collector current to flow duringthe MISFET operation as compared with cases in which an N-typesemiconductor substrate is used.

Also, in this embodiment, a gate insulating film 106 is formed on thebase region 103 so as to extend on part of the first emitter/sourceregion 104 and on a part of the extended drain region 102. However, itwould be sufficient if the gate insulating film 106 is formed at leaston a part of the base region 103 located closer to the collector region108 with respect to the first emitter/source region 104.

1. A semiconductor device comprising: a high-voltage semiconductorswitching element controlled by a gate voltage applied to a gateelectrode; and current detection means including a detection resistorcapable of detecting part of current flowing through the high-voltagesemiconductor switching element, wherein the high-voltage semiconductorswitching element includes: a base region of a second conductivity typeformed in a semiconductor substrate of a first conductivity type; afirst emitter region of the first conductivity type formed in the baseregion; a collector region of the second conductivity type formed in thesemiconductor substrate so as to be spaced apart from the base region; agate insulating film formed at least on a part of the base regionlocated closer to the collector region with respect to the first emitterregion; a gate electrode formed on the gate insulating film; a collectorelectrode formed above the semiconductor substrate and electricallyconnected with the collector region; and an emitter electrode formedabove the semiconductor substrate and electrically connected with boththe base region and the first emitter region; a second emitter region,which is electrically connected with the first emitter region throughthe detection resistor and is electrically connected with the currentdetection means, is also formed in the base region; and the emitterelectrode is not formed on the second emitter region, while the emitterelectrode is formed on a part of the base region that is adjacent to thesecond emitter region.
 2. The semiconductor device of claim 1, whereinthe semiconductor substrate is of the second conductivity type; thesemiconductor device further includes a drift region of the firstconductivity type formed in the semiconductor substrate so as to beadjacent to the base region; the first emitter region and the secondemitter region are spaced apart from the drift region; and the collectorregion is formed in the drift region.
 3. A semiconductor devicecomprising: a high-voltage semiconductor switching element controlled bya gate voltage applied to a gate electrode; and current detection meansincluding a detection resistor capable of detecting part of currentflowing through the high-voltage semiconductor switching element,wherein the high-voltage semiconductor switching element includes: abase region of a second conductivity type formed in a semiconductorsubstrate of a first conductivity type; a first emitter/source region ofthe first conductivity type formed in the base region; a collectorregion of the second conductivity type formed in the semiconductorsubstrate so as to be spaced apart from the base region; a drain regionof the first conductivity type formed in the semiconductor substrate soas to be spaced apart from the base region; a gate insulating filmformed at least on a part of the base region located closer to thecollector region with respect to the first emitter/source region; a gateelectrode formed on the gate insulating film; a collector/drainelectrode formed above the semiconductor substrate and electricallyconnected with the collector region and the drain region; and anemitter/source electrode formed above the semiconductor substrate andelectrically connected with both the base region and the firstemitter/source region; a second emitter/source region, which iselectrically connected with the first emitter/source region through thedetection resistor and is electrically connected with the currentdetection means, is also formed in the base region; and theemitter/source electrode is not formed on the second emitter/sourceregion, while the emitter/source electrode is formed on a part of thebase region that is adjacent to the second emitter/source region.
 4. Thesemiconductor device of claim 3, wherein the semiconductor substrate isof the second conductivity type; the semiconductor device furtherincludes a drift region of the first conductivity type formed in thesemiconductor substrate so as to be adjacent to the base region; thefirst emitter/source region and the second emitter/source region arespaced apart from the drift region; and the collector region and thedrain region are formed in the drift region.
 5. The semiconductor deviceof claim 3, wherein the collector region and the drain region eachinclude a plurality of separate parts; and each part of the collectorregion and each part of the drain region are located alternately so asto be in contact with each other in a direction perpendicular to adirection going from the collector region to the first emitter/sourceregion.
 6. The semiconductor device of claim 5, wherein the secondemitter/source region and the collector region are located so as to faceeach other with a part of the base region interposed therebetween. 7.The semiconductor device of claim 5, wherein the second emitter/sourceregion and the drain region are located so as to face each other with apart of the base region interposed therebetween.